Apparatus for removing metal from the surface of a metal object



March 25, 1958 F. E. CLARK ,7

APPARATUS FOR REMOVING METAL FROM THE SURFACE OF A METAL OBJECT FiledNbv. 26. 1954 2 Sheets-Shee t 1 ll/1mm INVENTOR BY ATTORNEY March 25,1958 F. E. CLARK 2,827,723

' APPARATUS FOR REMOVING METAL FROM THE 7 SURFACE OF A METAL OBJECTFiled Nov. 26. 1954 2 Sheets-Sheet 2 INVENTOR ATTORNEY United StatesPatent 6 F ice APPARATUS FOR REMCWKNG METAL FROM THE SURFACE OF A METAL()BJECT Fraii'cisE. Clark, San Gabriel, Caiif., assignor to TurcoProducts, Inc; LosAngeles, Calif a corporation of California ApplicationNovember 26, 1954, Serial No. 471,266

19Claims. (Cl. 41'-9) invention'relates to the etching or the removaljofmetaljfrom 'the surface ofa metal'object, e. g., one composed'of iron,nickel, titanium, magnesium, Zinc, aluminum or their alloys. Moreparticularly, the invention is concerned with novel apparatus andprocedure for this purpose, especially for the treatment of aluminum andits alloys.

It is known to etch acid soluble metals such as magne'sium, zincand'their alloys with an acid solution such as aqueous nitric acid. Itis also known to etch alkali soluble metals such as aluminum and itsalloys with a solution having a solvent action on the aluminum or alloysurface, such as a hot aqueous alkali solution, e. g., onecontaining'sodium or potassium hydroxide. One method 'of carryingout'the etching process employing acids is to immerse the'rn'etal partto be etched in the etching bath, while another'is to splash thesolution contained in a bath againstth'e work, the surface of which isto be etched or dissolved away, The prior art method for etching alkali'sol'uble metals'such as aluminum or its alloys is by immersion.

However, the use of the conventional methods, for example, immersion,for etching metal parts'often produces non-uniform etching and isdiflicult to control. V

Mc'ireover, where aluminum and its alloys are to be etched, conventionalprocedures have proved unsatisfactory because of the formation of aprecipitate of alumirium hydroxide and/ or hydrated aluminum oxides inthe solvent or etching bath, particularly when the concentration ofalkali in the solution is reduced due to the reaction of the alkali withthe metal. The formation of 'such precipitates not only interferes withthe action of the etching solution on the work but tends to form ascal'eon the etching tank or equipment which becomes most difiic'ult toremove. The precipitates tend to fill the tank and must be removedperiodically. Also, the strength of the solution gradually decreases andthe etchingsolu'tio'n' must be revitalized by addition of fresh or" itsalloys.

Another'object is to design novel apparatus particularly adapted for theunifornncontrolled etching or removal :ofn etai from the surface of awork piece composed of aluminum or its alloys.

A still further object of the invention is the provision ofn ovelapparatus for the eiiicient controlled removal of metal from the surfaceof an aluminum or aluminum .alloy part using a solvent or etching bath,including means for maintaining the bath substantially free of solids orfpr'ecipitate's which become suspendedin the"solvent bath.

V 2,827,723 Patented Mar. 25, 1958 placed overthejsurjfa'ce of the metalwork piece to produce the 'desiredetch pattern. V V

Yetcanotherfobject is to provide novel apparatus for theefiicientjetchingiorfremoval of metal fromthe surface of an aluminumalloy workpiece, by movemen'tfof ah alkali solution over thje work pieceunder-conditions to prevent substantial and uneven undercutting of themetal ofth'e work piece below and adjacent to'the'edgs ofamaskplacedtherebn, and includingmeans forthe rapid renijoval'o'f thesolids formedjinthe etching reaction from 7 said solution, and formaintaining the strength of"saidsolution I V V ,V

A st ill fur'theh objectis'the provision of procedure for the efii'cientremoval ofmetal from the'surface of a metal work piecesufch as aluminumor an aluminum alloy using a suitable solvent solution, which maintainsany undercutting'of th nifetal of the work piece beneaththe edges of themask 'uniform and'at a minimum.

A still further objectis to provide apparatus and procedu're forremoving precipitate formed in an etching reaction, for example," whenetching'aluminum or'its alloys with caustic alkali, from the etchingzone. A Other objects and advantages will become apparent from thefollowing descriptionofthe invention: According to the invention, metalsolvent or etching solution contained in a bath is caused to flowlaterally over the surface of a work piece properly mounted forthispurpose. The metal part to be etched maybe 'c ed on selectedportions of thesurface with a protectivemasking coating to inhibit orprevent attack by the etching agent while adjacent portions areavailable for such attack. Preferablyfthe work pieces are supported in areceptacle, the bottom of'which is disposed on an incline so that thesolution is conveniently conveyed by gravity into contact with the 'Workpieces. In' preferred practice, the work pieces are mounted so that thesurfac es to' be etched are in a plane parallel to the lateraldir'ection of flow of'thejetching solution. During flowi of theetchingsolutionabout and -over the surface of the work pieces, the latter arepreferably rotated to cancel out the directional etching eif ects of theliquid flow. I c

In this manner, while a certain amount of etching may take place underthe edges of a mask on the surfaces of the Work piece, rotation thereofwhile the solution is flowing thereover' renders such undercuttinguniform, and prevents the highly undesirable deep undercuttingjbeneathan edge of the mask facing opposite'to thedirectionof fluid flow, andsubstantially less undercutting beneath those edge portions of the maskfacing in the direction of flow of the solvent liquid. V I V Continuousmovement of the etching liquid overjthe surface of the metal work piecealso facilitates attack thereof by the solution in the selected,forexample, unmasked, areas of the work piece, and has a fi'ushingeffecton such surface. So-called smut and other precipitates loosened by thereaction, are carried away by this flushing action. This is notedparticularly where the work piece being processed is aluminum or analloy thereof, in which case such flushing action also aids inpreventing formation of adherent scale on thecontaining vessel. Sifnutappears on surfaces of aluminum alloys, particularly when aluminum isalloyed with" elements, such a's'for example, copper, iron and silicon,etc. Such aluminum alloys, when etched with caustic soda, producea'liilm which is black'a'n'd highly adherent to the surface'. Thesesmuts are insoluble in water and most acids. TIie'yJare soluble in HNOg,mixturescrnNogan-d "HgSOf'ndih v the, aforementioned solids, and foam..Solids. formedin the etching reaction become suspended in. the laterallyflowing stream of etching solutlonwhich flows at a, rate such as tomaintain the solidssuspended' at leastuntil the stream haspa'ssed'beyond the-etching zone so that essentially no solids drop tothe. bottom'of the receptacle,

,for example, trough, inthe etching zone. The resulting liquid mixturecontaining solids. or. precipitate 'such as I aluminum hydroxide and/oralumina formed in the e tching reaction and suspended in the bath, isremoved to a second zone maintained ate-lower temperature, wherein thesolids are settled out of the mixture and removed, and

the remainingclear liquor. is withdrawn. Such liquor ,can be added tothe solution, if desired, to replenish or may be recirculateddirectlytothe :bath, but is'first preferably conducted .to a third zone in whichmake-up or recesses 16 (see Fig. 4) are formed at intervals along thebottom of the trough, and a turntable 18 for supporting a work piece 29is positioned in each of wells 16. Three wells and turntables are shownin the instant embodiment, for convenience, but it is of courseunderstood that more or less than three such wellsand turntables can bedisposed along the bottom of the trough. Turntables 13 are eachsupported for rotation above the bottom of the wells by means of acentral shaft 22 passing through the bottom 1210f the trough normalthereto, 21 packing gland being provided between each of the shafts 22and the bottom of the trough to form a liquid seal. A motor (not shown)of low R. P. M. drives the turntables Why a system of belts 28 andpulleys 30 mounted on the lower ends of the shafts 22, the pulleys beingheld against longitudinal movement on such shafts by collars 32 fixed tothe shafts by set screws 34. A work piece 20, for example, having a mask21 thereon, which may be any suitable type of resist, is fastened toeach of the turntables 18 by any suitable means such as the rotatableclamps represented by numeral 36.

revitalize the main etching or solvent bath. The resulting solutioncauthen be heated to the proper temperature and recirculated to theetching bath in the first zone. The process of removal of solids andrecirculation of liquor to the bath-may be carried out eitherintermittently or continuously, preferably the latter.

The lower end of; the trough is pivotally supported on the uppershoulder of a vessel 39 by means of pivot pin 41, and the upper end ofthe trough is supported on a bracket 38 connected by a bolt 40 to avertical support '42, said support having a number of apertures 44there- 7 in to receive bolt 40 for adjustment of the height of'Apparatus foundparticularly advantageous forcarry- 1 ing out the aboveprocedure includes a trough, preferably inclined, in which arepositioned in spaced apart relation a series of preferably rotatablesupports or turntables on which the work pieces are designed to besupported Such supports vcan be rotated by a suitable drive, and meansare provided for feeding solvent or etching solution to the top of thetrough to permit such fluid to flow by gravity over, under and aroundthe rotating work pieces. Means are also included to adjust the amountoffeed and the. rate of efllux, and hence the depth of .the liquidflowing in the trough.

The lower end of the trough is connected to a settling vessel havingmeans therein to facilitate rapid settlingof any suspended solids in theliquid mixture conveyed from bracket 38 so as to impart to trough 10 anydesired degree of slope for adjusting the rate of flow of liquid alongthe trough. The slope of the'trough shown in the drawing is relativelylarge and favors a high rate of flow laterally over the surface of thework pieces. An-enclosure .6 is provided at the upper end of trough 10,and is formed by a rear wall 48, side Walls 50 (see Fig. 2), and aforward wall 52 of substantially less height than rear wall '48.

An adjustable plate or weir member54 is positioned on the forward wall52 of the enclosure 46. Plate 54 is provided near both ends thereof withtransverse slots 56 for the main tank, and means to permit withdrawal ofthe resultingclearliquor. Such liquor is then conductedto a make-uptankhaving agitating means, and'wher'ein make-upiliquid can be added tothe clear liquor'from the settling vessel. The resulting solution isthen pumped culation to the work pieces supportedin the trough.

' through a heater back to the top of the trough for recir- In theforegoing manner, .and particularly when aluminumparts are beingetchedusing an alkali solution,

precipitated material is rapidly and efficiently removed 7 inliquid'suspension from the. etching or treating zone to preventinterference of such material with the etching The invention will bemore clearly understoodby referment taken in connection with theaccompanying drawings wherein:

operation, and the' resulting clear solution substantially free ofsolids is recirculated to the etching zone.

. ence to the following description of .a preferred embodi- Fig. 1 is anessentially schematic assembly'view of the apparatus of the invention,shown mostly in section;

Fig. 2 is a section taken on line 2-2 of Fig. 1; Fig. 2a is a sectiontaken on line 2a2a of Fig. 2;

i Fig. 3 is a plan view of the trough shown in Fig. 1

taken on line 3.3 thereof; a r a Fig. 4 is a section taken on line 4-4of Fig. 3;

Fig. 5 is an enlarged section across a workpiece,"

taken on line 55 of Fig. 3; and V 7 Fig.6 is a cross section of 'a'trough and showing a modified structure for rotatably supporting the'work pieces in the trough. r r

Fig. 7 is a View taken on line 77 of Fig. 1'." Numeral 10 represents aninclined trough having a bottom 12 and A series of spacedwells receivingbolts 58 for securing plate 54 to wall 52 by means of nuts 60. It isseen that the height of the top edge 62 of plate 54 canbe varied bymoving such plate and the slots 56 therein vertically with respect tobolts '58, and tightening the nuts 60 at the desired vertical posi-"tion .of plate 54. Hence, it is seen that the amount and depth ofliquid flowing in trough 10 can be varied by adjustment of plate or Weir54.

Etching or solvent liquid is discharged through multiple pipes, oroutlets 64 from a manifold 66, into the tank or enclosure 46, from whichthe liquid flows over the top edge 62 ofplate 54 and into'the trough 10.The liquid circulates downward therein .by gravity, flowing around andover the turntables 18 and the work pieces 20 positioned thereon. As thework pieces rotate on the turntables, a small amount of substantiallyequal undercutting indicated at 68 and 69 in Fig. 5, takes place beneaththe inner opposite. edges 79 and 7 1,of the mask21. The :amount of suchundercutting is purposely exaggerated in Fig. 5 for illustration.

It is not essential in carrying out the invention that the work piecesbe rotated, especially when the surfaces to be etched are unmasked.However, such rotation is particularly advantageous where the partsbeing etched 'have masked or irregular surfaces where undercutting bythe laterally flowing etching solution will take place. Thus, if themasked workpieces 20. were not rotated according to theinvention, unevenand generally substantial undercutting wouldvtake place at 68 and 69.Thus, vsludge would tend to accumulate in the undercut beenath the.mask' edge '74 facing in the direction opposite to fluid the directionof fluid flow, hence producing uneven under- .cuts. 7 a

gate 72 is positionedacross the trough near, the

2,8 lower end thereof. The gate is mounted for vertical adjustment on apair of guide numbers 73 by means of nut and bolt assemblies 74, thebolts passing through slots 75 in the gate. By manipulating the bolts 74and moving the gate 72 up or down, the size of the opening 75 below thegate can be varied providing an additional means for controlling thedepth of liquid flow in the trough. I The employment of a laterallyflowing body of etching fluid according to the invention, permits theuse of trough with the work pieces in an inclined or horizontal positioninstead of the usual'etching tank with the parts in a vertical position.In addition to the other advantages previously noted, this feature ofthe invention permits the rapid disengagement of hydrogen gas formedduring etching from the surface of the etched part, whereas in theordinary etching tank containing a body of relatively quiescent liquid,and in which the etched body is suspended vertically, the hydrogen gastends to stream along the face of the work pieces.

The body of flowing liquid, for example, alkali solution, which reachesthe lower end of trough 10 following reaction of the alkali with thework pieces, for example, aluminum or an alloy thereof, has suspendedsolids therein which are formed in such reaction in the mannerpreviously noted. This liquid mixture is continuously dischargedinto thesettling vessel 39 on which the lower end of the trough 10 is supported.Vessel 39 has a scraper 76 positioned adjacent the bottom 78 of thevessel, the scraper being rotatably supported on a central shaft 80which is rotated by a pulley 82 driven by a belt 84 from a motor (notshown). The liquid mixture drops from the lower end of the trough 10through a cylindrical baflie 86 suitably mounted axially within vessel39 and passes downwardly to the lower portion of the vessel. The fluidthen rises in vessel 39 in the annular space 83 between the baflie 86and the side wall 90 of the vessel, and flows through an aperture 92 inthe upper end of wall 90, into an adjacent tank 94. The path of fluidflow is indicatedby the arrows in Fig. 1. In this manner the suspendedsolids are deposited at the bottom of vessel 39 and substantially clearliquor flows into the makeup tank 94.

Rotation of scraper 76 maintains the solids in a thick suspension atthebottom of vessel 39, and the solids are continuously discharged througha bottom outlet 96 of the vessel into a conveyor 98 having a screw feed100 which is driven by a motor 102, the solids being withdrawn at theopposite end of the conveyor.

The clear solution discharged into make-up tank 94 is agitated thereinby an agitator 104 driven by a motor 106 mounted at the bottom of thetank. Additional alkali solution may be introduced into tank 94 frompipe 112 by means of pump 114 and valve 116, to replenish the alkalilost in passage of the liquid through the system and by the etchingreaction in trough 10, while makeup water may be added through pipe 108,valve 110 and pipe 112.

The solution in tank 94 is discharged through pipe 118 into the intakeof pump 120, which pumps the liquid through valve 122 into a heater 124to bring the solution up to the desired temperature, and then circulatesthe heated liquid through pipe 126 connected to the manifold 66, andback into the tank 46 and trough10.

The process of the invention can thus be carried out by continuousoperation.

While turntables 18 have been shown as being supported for rotation onthe bottom of the trough 10, turntables or supports rotatably suspendedand driven from overhead can be utilized. Referring to Fig. 6 showing amodification of this type, numeral 130 represents a trough, preferablyinclined as in the case of trough 10. The trough 130 has vertical sides132 connected to its bottom 134, each of the sides 132 having a flange136 extending laterally along the upper edge thereof. A plurality ofU-shaped straps 138, one of which is shown in 6 Fig; 6, having flanges140 at the extremities of their legs 142, are connected at spacedintervals along the' sides 132 of trough by bolting the flanges 136 andof the trough and straps together withbolts 144.

Suspended from a thrust bearing positioned in a fixture 147 above thetank, and passing through a hearing 146 in the cross member148 of eachof the straps 133 is a vertically adjustable shaft 150 having connectedat its lower end clamps 152 and l53 for grasping and holding a workpiece 154 suspended in trough'130 above the bottom thereof. Clamp 153 islaterally adjustable along a plate 155 connected to shaft I'50, bymeansof the bolt and nut assembly 157 received in slot 159 at the upper endof clamp153'; A pulley 156 is keyed to the upper end of the shaft 150,and a belt- 158 driven bya motor (not shown) engages the pulley forrotationthereof and shaft 150. The fluid flowing in trough 1'30 belowand above the work piece 154- will etch either or both the upper andlower surfaces 160 and 162 of the work piece 154 according to theinvention, preferably while the work piece is being rotated. Accordingto the instant modification, it is seen thatby suspending'the workpieces from the supports or clamps 152 and 153 above the trough, thework pieces can be introduced into or removed from the laterally flowingstream of etchant without stopping the dew thereof and without requiringthe operator to place his hands in the etching liquid, by lifting shaft150 in its-bearings 1'45 and 146 sufiiciently to raise the clamps 152and work piece clear of the solution. Further, in themodification'of-Fig. 6, the trough 13.0'is free of structure at thebottom thereof, and this reduces any tendency to'trap precipitate alongthe bottom of the trough.

Although the invention has-been described above chiefly in connectionwith the etching of square'orrectangular metal plates, it is to beunderstood that metal parts or surfacesof other shapes, for example,circular or irregular, can beetched by means of the lateral flow etchingliquid concept of the invention, preferably but not necessarily inconjunction with rotation of the metal part.

In order to prevent or reduce the formation of hard, adherent scale,there may beadded to'the alkaline etching solution agents which keep theprecipitate floccul'ent.

According to the preferred embodiment of the invention for etching orremoving metal from an aluminum or aluminum alloy material, which isalkali soluble, a hot aqueous solution is generally employed'containingan'alkali such as sodium or potassium hydroxide, trisodiumphosphate, soda ash or the like, or mixtures thereof. Preferably, asodium hydroxide solution is used. Temperature of the solution isgenerally maintained in a range say from 100 F. to about boiling, duringtreatment, although lower temperatures may be used. Generally, thealkaliconcentrations employed in such solutions range from 0.1 to 10 normal,and if sludge modifiers "are used, they may be employed in amountssufficient to produce. a non-adherent sludge or precipitate, as forexa'inpie; 0.5% to 10% by weight of the alkali.

While the invention has been described particularly in' connection withthe etching of aluminum or an alloy thereof by means of alkali solution,it is of course un-' derstood that acid soluble metals such asmagnesium, iron, nickel, titanium and zinc can also be effectivelyetched by the apparatus and procedure disclosed herein, employing acidetchants such as aqueous nitric acid, hydrofluoric acid or mixturesthereof, depending on the particular metal, and if no sludge orprecipitate is formed in. the etching reaction, vessel 39 may beomitted. Also, it is noted that aluminum and its alloys may alsobeetched by means of an acid etching solution, such as hydrochloric acidor ferric chloride solution.

Instead of employing an inclined trough and gravity flow of-etchingliquid down said trough, it will be recognized by those skilled in theartthat I may use other means'to cause flow of etching liquid laterallywith respect to the rotating work pieces, .Thus,' foi' eiiample,turntables 18 can be mounted for rotation in a horizontal for rotationwithin the trough with the plane of such turntables horizontal and thusdisposed at an acute angle to the trough 10 and the direction of liquidflow therein.

While I have described a particular embodiment of my invention for thepurpose of illustration, it should be understood that variousmodifications and adaptations thereof may be made within the spirit ofthe invention as set forth in the appendedclaims.

I claim: a 1. A device for the removal of metal from a metal work piecewhich comprises an inclined trough, a rotatable support for said workpiece mounted in said inclined trough, means for rotating said supportand means for feeding a liquid to said inclined trough.

2. A' device for the removal of metal from a metal work piece whichcomprises an inclined trough, a rotatable supportfor said work piecemounted in said in- ,clined trough, means for rotating said support,means for feeding a metalsolvent liquid to said inclined'trough, andmeans for adjusting the depth of liquid flowing in said trough. V t l 73. A device for the removal of metal'froma metal work piece whichcomprises an inclined trough, a rotatable support for said work piecemounted in said inclined trough, means for rotating said support, meansfor feeding a metal solvent liquid to said inclined trough,

and means for recirculating liquid from the bottom of pieces whichcomprises. an inclined trough, 'a plurality of rotatable supports forsaid. workpieces mounted-along said trough, the plane of said supportsbeing substantially parallel to said trough, means for rotating saidsupports, means for feeding a, metal solvent liquid to said trough at apoint above the uppermost rotatable support in said trough, means foradjusting the depthof liquid in said trough, and means'for recirculatingliquid from the bottom of said. trough to saidiliquid'feeding means.

' 6QA devicefor the removal of metal frorna metal work piece whichcomprises a container, a, support for said work piece mounted in saidcontainer, means-for feeding liquid through a side of said container forlateral flowof said liquid over said support, means for removing saidliquid from a second'side of said container, a tank connected-to thesecondside 'of'said container, means insaidtank to permit settling of"solid material from a fluid :miXture discharged froms'aid container,means for drawing ofi substantially-clear liquid from said tank, andmeans' for recirculatingsaid clear liquid to said liquid feeding means;i I e 2 V 7."A device for the removaltofnretal'fromthesun face of ametal work piece comprises a conduit, a rota-table support for saidworkpiece mounted in said conduit, means for roitating'saidsupport,means for feeding a liquid to said conduit for lateral flow of saidliquid with respect to said support, a tai 1k connected to the dischargeend of'said Conduit, means in said tank to permit settling ofsolidmaterialifrom atfiuid mixture discharged from said conduit,means'for. drawing off substantially vessel connected to said outlet andmeans for recirculating liquid from said vessel to said liquid feedingmeans.

"clear liquid from said tank, and means for recirculating said clearliquid to saidliquid feeding means. 7

8. A device for the removalv of metalsfrom the surface of a metal workpiece whichcomprises' an inclined trough, a rotatable support for saidworkpiece mounted in said trough, means for rotating said support, meansfor feeding a metal solvent liquid to said trough, means for adjustingthe depth of liquid in said trough, a tank connected to the lower end ofsaid trough,, means in said tank to permit settling of solid materialfrom-a fluid mixture discharged from said trough, meansfordrawing ofisubstantially clear liquid from said tank, and means for recirculatingsaid clear liquid to said liquid feeding means.

9. A device for the removal of metal from the surface of a metal workpiece which comprises an inclined trough, a rotatable support for saidwork piece mounted in said trough, means for rotating said'support,means for feeding a metal solvent liquid to said trough, means foradjusting the depth of liquid in said trough, a tank connected to thelower end of said trough, means in said tank to permit settling of solidmaterial from a fluid mixture discharged from said' trough, means fordrawing off substantially clear liquid from an Outlet in said tank, aliquid make-up it). A device for the removal of metal from metal workpieces which comprises an inclined trough, ,a plurality of rotatablesupports for said work pieces mounted along said trough, substantiallyparallel thereto, means for rotating said supports, means for feeding aliquid to said trough at a point above the uppermost rotatable supportin said trough, a tank connected to the lower end' of said trough,means. in said tank to permit settling of solid material from a fluidmixture discharged from said trough, means for'drawing off substantiallyclear liquid from said tank and means for recirculating said'clearliquid to said liquid feeding means.

11. A device for the removal of metal from metal work pieces whichcomprises an inclined trough, a plurality of rotatable supports for saidworkpieces, said supports being suspended over said trough and spacedfrom each other therealong, means for rotating said supports, means forfeeding a liquid to said trough at a point above the uppermost rotatablesupport in said'trough, means for adjusting the depth of liquid in saidtrough, a tank connected to the lower end of said trough, .meansin .saidtank to permit settling of solid materialfrom a fluid mixture dischargedfrom said trough, means for drawing face of metal work piecestwhichcomprises'an inclined ,trough, a plurality of turntables mountedalongsaid trough for supporting said work pieces, means for driving saidturntables, means for feeding a metal solvent liquid to said trough ata'point above theuppermost turntable in said trough, means for adjustingthe depth of liquid in said trough and means for recirculating liquid 1from the bottom of said troughto'said-liquid feeding means. a V

13. A device 'for'the'removal ofjmetal from the surface of metal workpieces which comprises an inclined trough,

a plurality of turntables mounted along said trough for supporting saidwork pieces, the plane of said turntables being substantially parallelto said trough, means for driving said turntables, means for feeding ametal solvent liquid to said trough at' a point above the uppermostturna table in said trough, means for adjusting the depth of liquid insaid trough, ja'tank connectedto the lower end of said trough, arotatable scraper positioned adjacent the bottom of said tank, means forrotating said scraper, a

:bafie adjacent the inlet to said tank for directingincorning.

fluid downward in said tank, means for drawing ofi liquid from an outletin said tank in the upper portion thereof, a screw conveyor connected tothe bottom of said tank for withdrawing solid material therefrom, aliquid makeup vessel connected to said outlet of said tank, an agitatorin said vessel and means for recirculating liquid from said vessel tosaid liquid feeding means.

14. A device for the removal of metal from the surface of metal workpieces which comprises an inclined trough, a plurality of turntablesmounted along said trough for supporting said work pieces, means fordriving said turntables, means for feeding a metal solvent liquid tosaid trough at a point above the uppermost turntable in said trough, anadjustable weir positioned above said uppermost turntable forcontrolling the depth of liquid in said trough and means forrecirculating liquid from the bottom of said trough to said liquidfeeding means.

15. A device for the removal of metal from the surface of metal workpieces which comprises an inclined trough, a plurality of turntablesmounted along said trough for supporting said work pieces, means fordriving said turntables, means for feeding a metal solvent liquid tosaid trough at a point above the uppermost turntable in said trough, anadjustable weir positioned above said uppermost turntable adjacent theupper end of said trough, an adjustable gate positioned adjacent thelower end of said trough, said weir and gate permitting control of thedepth of liquid in said trough, and means for recirculating liquid fromthe bottom of said trough to said liquid feeding means.

16. An apparatus for the removal of metal from a metal work piececomprising, a tank forming a reservoir for liquid etching solution, saidreservoir having an inlet at one end thereof and an outlet atsubstantially the opposite end thereof for said solution, means forsupporting said work piece in said reservoir, means for rotating saidsupporting means, and means for continuously flowing a stream of saidsolution through said reservoir from said inlet to said outlet, wherebysaid work piece is etched by said solution by contact with said solutionflowing through said reservoir.

17. An apparatus as defined in claim 16, and further including means forregulating the depth of said solution flowing through said reservoir.

18. An apparatus as defined in claim 16, and further including means forseparating solids from said etching solution, and means for conductingsaid solution from said reservoir to said separating means.

19. An apparatus as defined in claim 18, and further including means forrecirculating the solution from said separating means to said inlet insaid reservoir.

References Cited in the file of this patent UNITED STATES PATENTS1,166,378 Levy Dec. 28, 1915 2,141,162 Brandt Dec. 27, 1938 2,194,607McDevitt Mar. 26, 1940 2,568,803 Guenst Sept. 25, 1951 2,592,729 PennellApr. 15, 1952 FOREIGN PATENTS 388,411 France May 30, 1908

